1. Field of the Invention
The present invention relates to a portable terminal, and more particularly to an apparatus for controlling the output of image data to drive a display unit in a portable terminal with the display unit.
2. Description of the Related Art
A display unit, such as a liquid crystal display (LCD), is typically used in a portable terminal, such as a mobile telephone, personal digital assistant (PDA) or the like, to display images.
In such a portable terminal, as shown in FIG. 1, a host processor 100 outputs image data for a screen to be displayed through an LCD panel 106, to a display data buffer 104 in an LCD driver 102 to construct the screen. The host processor 100 is typically a microprocessor, and the display data buffer 104 is typically a video random access memory (RAM) for buffering image data on a screen basis. In the case where the portable terminal has an on-screen display (OSD) function, the host processor 100 also outputs OSD image data to an OSD application specific integrated circuit (ASIC) chip to construct a screen. On the other hand, for screen updating, the host processor 100 outputs image data for a new screen for every screen to the display data buffer to construct the new screen, so as to update a current screen with the new screen.
Recently, on the other hand, a color LCD has increasingly been employed as the display unit in the portable terminal as described above, and also in a moving image-type mobile communication terminal. In the case where the portable terminal has the color LCD, the host processor must output an increased amount of image data for display of one screen, with the increase in resolution of the color LCD. However, the microprocessor, which is used as the host processor in the portable terminal, is limited in its performance.
For this reason, the output of image data for a new screen for every screen to the display data buffer for screen updating acts as a load on the microprocessor, resulting in a reduction in processing rate thereof and, in turn, a screen ripple or flickering phenomenon, causing irritation to a user's eyes. For example, in the case where the user scrolls up or down on a menu screen, the entire screen must be updated. In this case, due to the limitations in the performance of the microprocessor employed in the portable terminal, the screen ripple phenomenon is visible to the user's eyes during the screen updating. Furthermore, when the scrolling is rapidly conducted, a screen update speed responsive thereto does not follow a user input speed. Moreover, when an incoming call animation, an outgoing call animation, etc. are displayed, the screen ripple or flickering phenomenon also occurs during the screen updating.